In the prior art, it has been a common practice to puff cereal grains by means of an explosion process in which a batch of grain is heated under gas (steam) pressure in a sealed tubular chamber of a puffing fun for a predetermined length of time. After a quantity of the grain has been sufficiently heated and the pressure and temperature within the gun chamber has reached a suitable level, the chamber is quickly opened to atmospheric pressure thus effecting a sudden expansion or "puffing" of the cereal grains which are then violently ejected from the chamber into a receiving bin or the like.
A common puffing gun consists of a sealable, long-sized rotating drum having strong construction for safety reasons, given the great stresses created on the gun by the explosive puffing action with each firing or shot. A typical puffing operation comprises the successive steps of loading, closing, heating, pressurizing and releasing for each batch to be processed. The execution of each of these steps in a convenient manner requires the addition of a number of auxiliary devices and mechanical equipment which renders the typical puffing gun a mechanically complex and heavy piece of equipment. For example, rotation of the drum, which is necessary for efficient and rapid heating of a loaded grain batch and to prevent burning of the grains, requires the addition of suitable rotating and support means for the drum. Heating requires the addition of proper heating means outside the drum, usually in the form of gas burners positioned underneath and circumferentially about the drum, or a heating furnace that encloses the rotatable drum. Given the rotation of the gun barrel, the pressure gas, usually steam, must enter at one side through a central longitudinal axis thereof and thereby necessitates a special inlet connection. The opposite side of the barrel must be closed by a sealing/hinged lid or cover, actuated by an appropriate mechanism. Because the firing position of the gun is essentially horizontal, efficient loading of a quantity of grains requires tilting of the drum and thus a pivotable supporting frame therefor. Such a gun construction is for example described in the Warren patent U.S. Pat. No. 2,116,212 and further improved J. J. von Edeskuty in U.S. Pat. No. 2,803,576. An improved closing mechanism is, for example, disclosed in EP 0,374,358.
The prior art devices are voluminous and expensive and require a lot of maintenance. Operational control and flexibility during use are rather poor. Furthermore, the prior art devices cannot be significantly increased in production capacity since enlarging the size of the gun and auxiliary mechanics leads to the huge, heavy constructions required to accommodate the increased violence of puffing explosions. The total process time per batch puffed with a conventional gun may amount to 7-10 minutes.